HYDROLYSIS OF CHROME SHAVINGS - APPLICATION OF COLLAGEN HYDROLYSATE AND ACRYLIC-PROTEIN IN POST TANNING OPERATIONS

The tanning industry is a generator of liquid wastes as well as tanned and non-tanned solid wastes plus those derived from the waste water t reatment plant. This situation requires the introduction of ''cleaner leather technologies'' and of treatment systems for both effluents and solid wastes, so that pollutant discharge standards can be reached. P articularly, solid wastes from chrome tanned leather require special a ttention because of their volume and of the requirements by authoritie s for their direct disposal in landfill sites. A technological alterna tive for upgrading these wastes is the detanning of chrome shavings (a nd wet-blue trimmings) through alkaline hydrolysis assisted by the act ion of proteolytic enzymes at a moderate temperature (55 degrees C), s o as to obtain a collagen hydrolysate and a ''chrome cake'', both with potential applications in the tanning industry. This paper describes experiments performed in the application of collagen hydrolysates and of ''acrylic-protein'' polymers (acrylic acid/hydrolysed collagen poly mers) in post-tanning processes for the manufacture of bovine leather for ''softy'' uppers. The retanning capacity of synthesized polymers a nd the positive effects attained from hydrolysates in the fatliquoring process (''nutrient and cosmetic effects'') were assessed by means of a subjective evaluation and through a statistical analysis of the phy sico-mechanical strengths of the leathers. Results are also shown from a laboratory test with chrome tanned hide powder aimed at assessing t he ''retanning degree'' of these products. The test was developed to a llow the comparison of the retanning agents under analysis and to comp lement the retanning test.